In today's environment, a server computer system often includes several components, such as the server itself, hard drives, or other peripheral devices. These components are generally stored in racks. For a large organization, the storage racks can number in the hundreds and occupy huge amounts of expensive floor space. Also, because the components are generally free standing components (i.e., they are not integrated), resources such as disk drives, keyboards, and monitors cannot easily be shared. Blade servers have been developed to bundle the server computer system described above into a compact operating unit. A blade server may be a high-density, rack-mounted packaging architecture for servers that provides input/output (I/O), systems management, and power to individual blades. Blades may include servers, processor nodes, storage nodes, or other components and may each plug into and operationally connect to the blade server to share in resources such as power, cooling, network connectivity, management functions, and access to other shared resources (such as a front-panel or CD-ROM drive). One feature of blade servers is that individual blades may be ‘hot swapped’ without affecting the operation of other blades in the system. An administrator or other user may simply remove one blade (such as one that is inoperable or that will be replaced) and place another in its place. An example blade server is International Business Machines (IBM®) Corporation's IBM eServer™ BladeCenter® system, a high-density, rack-mounted packaging architecture for servers that provides I/O, systems management, and power to inserted blades.
In server design, as in the design of many other types of computer systems, there is a trend towards higher densities of components. For example, it is often desirable to put a greater number of server blades into a package of given size. Additionally, server designers (similarly to designers of other computer systems) continue to increase performance of server components in order to meet customer needs. In combination, the higher component densities and increased performance of components result in an increased need for cooling of the servers and their components. Such increased cooling needs are likely to continue to rise as component densities and performance both increase. Accordingly, blade servers typically cool their component blades by drawing air through the chassis of the blade server and thus through each blade (or fillers) via the use of blowers in a front-to-back blade cooling pattern. For many blade server designs, the blowers are required to be invertible so that the blower functions properly in both the standard and inverted positions.
One problem with blowers is that, in the event of failure of the blower fan, air may recirculate back into a blower through its exhaust. While this problem can occur with blowers in any system, this problem is exacerbated for blade server blowers because blower air inlets typically face each other and hot exhaust air recirculating through a failed blower will negatively impact the performance of the other blower. In this situation, the remaining functional blower draws air from the back of the system through the failed blower and exhausts it out the back again, severely reducing the flow of cooling air through the blade system as a whole. Designers have provided one solution to this problem by providing a backflow damper with a frame and several pivoting vanes that are installed horizontally. In the event of blower failure, these pivoting vanes utilize gravity to close when blower air no longer keeps them open (i.e., after blower failure) and thus prevent recirculation of air back into the blower. This solution, however, greatly increases the impedance of the air exiting the blower as the air exiting, the blower must overcome the gravitational forces on the vanes. Moreover, an extra vane must be added to the last position to satisfy the inversion requirement, increasing the cross-sectional ‘blockage’ of the blower exhaust and thus increasing the impedance.
Another solution to the problem of blower exhaust backflow is to use a single large vane installed vertically on either side of the frame that is spring-loaded to close when the blower fails. This solution satisfies the inversion requirement but also greatly increases the impedance of the backflow damper as the air exiting the blower must overcome the spring force, which must be relatively large to close the vane during failure and during shipping. There is, therefore, a need for an effective and efficient system to preventing exhaust backflow from a blower.